Non-sustainable food choices are responsible for many global challenges, such as biodiversity loss and climate change. To achieve a transformation toward sustainable nutrition, it is crucial to implement education for sustainable development (ESD), with the key issue "nutrition", in schools and teacher training. Biology teachers are crucial for promoting ESD competences. Thus, the main aim of the study is to investigate the social and environmental psychological factors that may affect the intention of student biology teachers to eat sustainably as an integral part of their action competence needed for teaching this topic effectively. We conducted a paper-pencil questionnaire (N = 270, Mage = 22.9; SD = 2.8) based on the theory of planned behavior (TPB) and expanded the model by integrating environmental concern and nature relatedness. A path model is reported to show the relationships between the variables. The results show that the extended TPB model is suitable for predicting the intention to eat sustainably. Nature relatedness and altruistic concern positively predict attitudes and the intention to eat sustainably. This study suggests further research on the importance of (student) teachers' nutritional behavior, as a possible determinant of the intention to teach this topic in their future school career. © 2020 by the authors.